The datanode now performs 4MB readahead by default when reading data from its disks, if the native libraries are present. This has been shown to improve performance in many workloads. The feature may be disabled by setting dfs.datanode.readahead.bytes to "0".

The datanode now performs 4MB readahead by default when reading data from its disks, if the native libraries are present. This has been shown to improve performance in many workloads. The feature may be disabled by setting dfs.datanode.readahead.bytes to "0".

Description

The fadvise features have been implemented for some time, and we've enabled them in production at a lot of customer sites without difficulty. I'd like to enable the readahead feature by default in future versions so that users get this benefit without any manual configuration required.

The other fadvise features seem to be more workload-dependent and need further testing before enabling by default.